Non-synchronous control of laser diode

ABSTRACT

A system and method for non-synchronously projecting light in an imaging system is provided. A pixel panel may be selectively controlled to direct light onto or away from a subject. A light source, such as a laser diode, projects light pulses at the pixel panel. The pulses are not synchronized with the pixel panel, so the light may strike the pixel panel at any time when the pixel panel is operable to direct light towards the subject. The pulses may be constant or variable in energy or duration, depending on the desired results.

BACKGROUND

[0001] The present invention relates generally to imaging systems, andmore particularly, to a system and method for controllably projectingand redirecting light.

[0002] Digital systems, such as those used in maskless photolithographicprocessing, typically utilize a light source to project a light onto apixel panel. The pixel panel may then be controlled, for example, toeither reflect the light onto a subject or away from the subject.Therefore, the projected light may remain relatively constant while thepixel panel controls whether the light is “on” (directed toward thesubject) or “off” (directed away from the subject).

[0003] However, using the pixel panel to control the light may produce anumber of undesirable results. For example, the fact that the lightprojected by the light source is relatively constant produces largeamounts of heat, which may interfere with the proper operation of thesystem. The produced heat also requires equipment to aid in itsdissipation, which increases the cost and complexity of the system. Inaddition, the operation of the pixel panel may create undesirableeffects on the subject as it transitions between reflecting the lighttoward and away from the subject.

[0004] One way to overcome some of the above difficulties is to turn thelight source on and off in synchronization with the pixel panel.However, it may be difficult to synchronize the light source with thepixel panel, due in part to the speed with which the pixel panel maytransition from on to off and vice versa.

[0005] Therefore, certain improvements are needed in controllablyprojecting light toward a subject. For example, it is desirable toproject the light onto the pixel panel non-synchronously. It is alsodesirable to lower the heat produced by the light source, to lower thepower required by the light source, and to be more efficient.

SUMMARY

[0006] A technical advance is provided by a novel system and method fornon-synchronously projecting light onto a subject in an imaging system.In one embodiment, the method includes providing a light source operableto project light in pulses and providing a pixel panel to selectivelydirect the projected light towards the subject. The method determines atleast a first period and a second period during which the pixel paneldirects the projected light towards the subject, where the first andsecond periods each have a start time. During the first period, thelight is projected in at least one pulse towards the pixel panel at afirst time relative to the start of the first period. During the secondperiod, the light is projected in at least one pulse towards the pixelpanel at a second time relative to the start of the second period,wherein the first and second times are not synchronized relative to thestart of the first and second periods.

BRIEF DESCRIPTION OF DRAWINGS

[0007]FIG. 1 is a diagrammatic view of an improved digitalphotolithography system for implementing various embodiments of thepresent invention.

[0008]FIG. 2 illustrates an exemplary point array aligned with asubject.

[0009]FIG. 3 illustrates the point array of FIG. 2 after being rotatedrelative to the subject.

[0010]FIG. 4 illustrates an exemplary imaging system utilizing aconventional light source.

[0011]FIG. 5 illustrates a portion of an imaging system utilizing alaser diode array.

[0012]FIG. 6 illustrates the laser diode array of FIG. 5.

[0013]FIG. 7 illustrates utilizing the laser diode array of FIG. 6 as ahigh power light source.

[0014]FIG. 8 illustrates the imaging system of FIG. 4 utilizing a laserdiode as a light source.

[0015]FIG. 9 is a graph illustrating the relationship between a DMDstate and a laser diode signal, where the laser diode signal includespulses of equal duration and energy.

[0016]FIG. 10 is a graph illustrating the relationship between a DMDstate and a laser diode signal, where the laser diode signal includespulses of variable duration and energy.

DETAILED DESCRIPTION

[0017] The present disclosure relates to imaging systems, and moreparticularly, to a system and method for controllably projecting andredirecting light. It is understood, however, that the followingdisclosure provides many different embodiments, or examples, forimplementing different features of the invention. Specific examples ofcomponents and arrangements are described below to simplify the presentdisclosure. These are, of course, merely examples and are not intendedto be limiting. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition is forthe purpose of simplicity and clarity and does not in itself dictate arelationship between the various embodiments and/or configurationsdiscussed.

[0018] Referring now to FIG. 1, a maskless photolithography system 100is one example of a system that can benefit from the present invention.In the present example, the maskless photolithography system 100includes a light source 102, a first lens system 104, a computer aidedpattern design system 106, a pixel panel 108, a panel alignment stage110, a second lens system 112, a subject 114, and a subject stage 116. Aresist layer or coating 118 may be disposed on the subject 114. Thelight source 102 may be an incoherent light source (e.g., a Mercurylamp) that provides a collimated beam of light 120 which is projectedthrough the first lens system 104 and onto the pixel panel 108.Alternatively, the light 102 source may be an array comprising, forexample, laser diodes or light emitting diodes (LEDs) that areindividually controllable to project light.

[0019] The pixel panel 108, which may be a digital mirror device (DMD),is provided with digital data via suitable signal line(s) 128 from thecomputer aided pattern design system 106 to create a desired pixelpattern (the pixel-mask pattern). The pixel-mask pattern may beavailable and resident at the pixel panel 108 for a desired, specificduration. Light emanating from (or through) the pixel-mask pattern ofthe pixel panel 108 then passes through the second lens system 112 andonto the subject 114. In this manner, the pixel-mask pattern isprojected onto the resist coating 118 of the subject 114.

[0020] The computer aided mask design system 106 can be used for thecreation of the digital data for the pixel-mask pattern. The computeraided pattern design system 106 may include computer aided design (CAD)software similar to that which is currently used for the creation ofmask data for use in the manufacture of a conventional printed mask. Anymodifications and/or changes required in the pixel-mask pattern can bemade using the computer aided pattern design system 106. Therefore, anygiven pixel-mask pattern can be changed, as needed, almost instantlywith the use of an appropriate instruction from the computer aidedpattern design system 106. The computer aided mask design system 106 canalso be used for adjusting a scale of the image or for correcting imagedistortion.

[0021] In some embodiments, the computer aided mask design system 106 isconnected to a first motor 122 for moving the stage 116, and a driver124 for providing digital data to the pixel panel 108. In someembodiments, an additional motor 126 may be included for moving thepixel panel. The system 106 can thereby control the data provided to thepixel panel 108 in conjunction with the relative movement between thepixel panel 108 and the subject 114.

[0022] Efficient data transfer may be one aspect of the system 106. Datatransfer techniques, such as those described in U.S. provisional patentapplication Serial No. 60/278,276, filed on Mar. 22, 2001, and alsoassigned to Ball Semiconductor, Inc., entitled “SYSTEM AND METHOD FORLOSSLESS DATA TRANSMISSION” and hereby incorporated by reference as ifreproduced in its entirety, may be utilized to increase the throughputof data while maintaining reliability. Some data, such as highresolution images, may present a challenge due in part to the amount ofinformation needing to be transferred.

[0023] The pixel panel 108 described in relation to FIG. 1 has a limitedresolution which depends on such factors as the distance between pixels,the size of the pixels, and so on. However, higher resolution may bedesired. Such improved resolution may be achieved as described below andin greater detail in U.S. patent Ser. No. 09/923,233, filed on Aug. 3,2001, and also assigned to Ball Semiconductor, Inc., entitled “REAL TIMEDATA CONVERSION FOR A DIGITAL DISPLAY” and hereby incorporated byreference as if reproduced in its entirety.

[0024] Referring now to FIG. 2, the pixel panel 108 (comprising a DMD)of FIG. 1 is illustrated. The pixel panel 108, which is shown as a pointarray for purposes of clarification, projects an image (not shown) uponthe subject 114, which may be a substrate. The substrate is moving in adirection indicated by an arrow 214. Alternatively, the point array 108could be in motion while the substrate 114 is stationary, or both thesubstrate 114 and the point array 108 could be moving simultaneously.The point array 108 is aligned with both the substrate 114 and thedirection of movement 214 as shown. A distance, denoted for purposes ofillustration as “D”, separates individual points 216 of the point array108. In the present illustration, the point distribution that isprojected onto the substrate 114 is uniform, which means that each point216 is separated from each adjacent point 216 both vertically andhorizontally by the distance D.

[0025] As the substrate 114 moves in the direction 214, a series of scanlines 218 indicate where the points 216 may be projected onto thesubstrate 114. The scan lines are separated by a distance “S”. Becauseof the alignment of the point array 108 with the substrate 114 and thescanning direction 214, the distance S between the scan lines 218 equalsthe distance D between the points 216. In addition, both S and D remainrelatively constant during the scanning process. Achieving a higherresolution using this alignment typically requires that the point array108 embodying the DMD be constructed so that the points 216 are closertogether. Therefore, the construction of the point array 108 and itsalignment in relation to the substrate 114 limits the resolution whichmay be achieved.

[0026] Referring now to FIG. 3, a higher resolution may be achieved withthe point array 108 of FIG. 2 by rotating the DMD embodying the pointarray 108 in relation to the substrate 114. The rotation is identifiedby an angle θ between an axis 310 of the rotated point array 108 and acorresponding axis 312 of the substrate. As illustrated in FIG. 3,although the distance D between the points 216 remains constant, such arotation may reduce the distance S between the scan lines 218, whicheffectively increases the resolution of the point array 108. The imagedata that is to be projected by the point array 108 must be manipulatedso as to account for the rotation of the point array 108.

[0027] The magnitude of the angle θ may be altered to vary the distanceS between the scan lines 218. If the angle θ is relatively small, theresolution increase may be minimal as the points 216 will remain in analignment approximately equal to the alignment illustrated in FIG. 2. Asthe angle θ increases, the alignment of the points 216 relative to thesubstrate 114 will increasingly resemble that illustrated in FIG. 3. Ifthe angle θ is increased to certain magnitudes, various points 216 willbe aligned in a redundant manner and so fall onto the same scan line218. Therefore, manipulation of the angle θ permits manipulation of thedistance S between the scan lines 218, which affects the resolution ofthe point array 108. It is noted that the distance S may not be the samebetween different pairs of scan lines as the angle θ is altered.

[0028] Referring now generally to FIGS. 4a-c, in one embodiment, theoperation of the photolithography system 100 of FIG. 1 is illustratedutilizing a conventional light source 410 to continuously project lightduring the operation of the system 100. In operation, the system 100utilizes the light source 410 to direct light through the lens system104 (shown as pair of lenses) and onto a reflective device 412 (notshown in FIG. 1) such as a mirror. The mirror 412 reflects the lightonto the pixel panel 108, which may be a DMD. It is noted that the DMD108 may be rotated to provide a desired resolution as described inreference to FIGS. 2 and 3. The light striking the DMD 108 is partiallydiffracted and scattered. The DMD 108 may selectively direct the lightthrough a series of optical devices 112 and onto the subject 114 such asa substrate (in which case the DMD 108 will be referred to as “on”) ormay direct the light away from the substrate 114 (in which case the DMD108 will be referred to as “off”). The light is to strike the substrate114 at a desired location 414.

[0029] Referring now specifically to FIG. 4a, the conventional lightsource 102 is projecting light, but all the pixels in the DMD 108 areoff and so the light is reflected away from the substrate 114 asindicated by the reference number 418. Referring now to FIG. 4b, the DMD108 is in a transition state between off (FIG. 4a) and on (FIG. 4c).During this transition, the light which is projected from the lightsource 102 and reflected by the mirror 412 onto the DMD 108 is partiallydirected toward the substrate 114. However, because the transitionperiod is not instantaneous, a portion of the light reflected duringthis time may not be properly directed by the DMD 108 toward thesubstrate 114. For example, the light may strike a location 416. Thisresults in a blurring effect on the substrate 114, which is causedpartially by the continuous projection of light onto the DMD 108 duringits transition period. Referring now to FIG. 4c, the DMD 108 is on andthe light is directed toward the location 414 on the substrate 114 asdesired.

[0030] Referring now to FIG. 5, in another embodiment, a portion of thephotolithography system 100 is illustrated using an LED array or a laserdiode array 510 (both of which are hereinafter referred to as a laserdiode array for purposes of clarity and described later in greaterdetail) as the light source 102 of FIG. 1 rather than the conventionalMercury lamp described previously. The laser diode array may be utilizedto project light onto the pixel panel 108, which may be rotated asdescribed in reference to FIGS. 2 and 3. As will be described in greaterdetail in relation to FIGS. 8a-c, higher resolution is possible using alaser diode because the light can be turned off during the mirrortransition, reducing diffracted and scattered light. This aids inovercoming the blurring illustrated in the above discussion of FIGS.4a-c. In addition, a smaller light source (as compared to a conventionalMercury arc lamp) improves the optical resolution by reducing the spotsize at the focal point of the micro-lens array. Combining a laser diodewith the rotation of a pixel panel as described in reference to FIGS. 2and 3 may provide additional resolution benefits.

[0031] Although other relationships may be desirable, there may be aplurality of individual laser diodes for each pixel of the pixel panel108. This enables the laser diode array 510 to provide higher exposurecontrast because individual diodes may be selectively pulsed on and offto accommodate for the desired contrast level and field uniformity. Inthis way, if certain pixels of the pixel panel 108 are “dull,” morelight can be provided to these pixels, than to other less-dull pixels.This can also solve other problems that affect the contrast level.

[0032] Referring now to FIG. 6, the laser diode array 510 of FIG. 5 isillustrated in greater detail. The laser diode array 510 comprises aplurality of laser diodes 512 embedded within or connectable to asubstrate 514, which includes embedded circuitry 520. The circuitry 520,which may include embedded microelectronics and electrical connectors,is operable to provide parallel and/or serial control signals and/oraddress lines to the laser diode array 510. These control signals mayenable the regulation of the wavelength and/or intensity of laser beamsproduced by the laser diode array 510. Connectable to the substrate 514is a connector 516, which enables a computer aided design system (notshown) to control the laser diode array 510 through the circuitry 514.Proximate to the substrate 514 is a cooler 518, which may be athermo-electric cooler such as a Peltier cooler. The cooler 518 permitsuniform cooling to stabilize the performance of the laser diode array510. The laser diode array 510 may also include memory (not shown),either embedded into the substrate 514 or made accessible to the array510 using other common techniques.

[0033] Referring again to FIG. 5, the operation of a single laser diode512 a from the laser diode array 510 is described. The laser diode 512 aprojects a laser beam 520, which may be of varying wavelengths andintensity. The wavelength and intensity of the beam 520 may be alteredto achieve a desired result. For example, the intensity and/orwavelength of the beam 520 may be altered by regulating the currentsupplied to the laser diode 512 a. Such regulation may be exercised onan individual diode basis or multiple laser diodes 512 may be controlledat once.

[0034] The shape of the beam 520 projected by the laser diode 512 andreflected off the pixel panel 108 may be distorted relative to somedesired beam shape, and so may require correction. Therefore, the beam520 may be passed through the lens system 112 of FIG. 1, which mayinclude a plurality of optical devices, including an aspherical orcylindrical lens array 522 to reshape the beam into the desired shape.For example, the laser diode 512 a may produce a beam 520 having an ovalshape, instead of a desired circular shape. Therefore, the lens array522 may be utilized to reshape the oval beam into a circular beam. Oncethe laser beam 520 is reshaped, it passes through a pair of lenses 524,526 and then a micro-lens array 528. The micro-lens array 528, which isa multi-focus device, may produce a one or two dimensional point array.The beam 520 then passes through a grating 530, which may take onvarious forms, be placed in alternate locations, and in someembodiments, may be replaced with another device or not used at all. Thebeam 520 then passes through a second set of lenses 532, 534 beforestriking the surface of a subject 536.

[0035] Referring now to FIG. 7, in yet another embodiment, the laserdiode array 510 of FIGS. 5 and 6 may be utilized as a high power lightsource 700 by combining the output of multiple laser diodes 512. Thelaser diodes 512 of the array 510, of which only ten are illustrated forthe sake of clarity, project laser beams 720. The beams 720 first passthrough a lens array 722 for any desired reshaping of the beams 720 asdescribed above in reference to FIG. 5. The beams 720 then pass througha micro-lens array 724. The micro-lens array 724 provides enhancedcoupling between the laser diodes 712 and multiple multimode opticfibers 726. The fibers 726 may be bundled into one or more outputs,which may transfer the light to optics for beam reshaping,decorrelation, and/or the application of other techniques. The outputmay be used for photolithography, as a laser pump for other lasingmedia, or in a variety of other applications where such a high powerlight source may be desired.

[0036] A variety of embodiments illustrating various approaches forimplementing laser diodes in a photolithography system are described inadditional detail in U.S. provisional patent application Serial No.60/274,371, filed on Mar. 8, 2001, and also assigned to BallSemiconductor, Inc., entitled “HIGH POWER INCOHERENT LIGHT SOURCE WITHLASER ARRAY” and U.S. patent application Ser. No. 09/820,830, filed onMar. 28, 2001, and also assigned to Ball Semiconductor, Inc., entitled“INTEGRATED LASER DIODE ARRAY AND APPLICATIONS”, both of which arehereby incorporated by reference as if reproduced in their entirety.

[0037] Referring now generally to FIGS. 8a-c, in one embodiment, thephotolithography system 100 of FIG. 4a-c is illustrated utilizing alaser diode 810 rather than the conventional light source 410. The laserdiode 810 may be operated in the same manner as the conventional lightsource 410 (i.e., in a relatively continuous manner using a continuouswave mode), or may be operated in a pulse mode which allows the laserdiode 810 to be turned on and off as desired. The laser diode 810 isable to pulse at an extremely high frequency (e.g., in the gigahertzrange).

[0038] Utilizing the laser diode 810 in pulse mode may provide a higheraverage power delivery than continuous wave mode. In addition, thepulsing may increase the lifetime of a pixel panel due in part toreduced turn-on time. The pulsing may also reduce the amount of heatproduced by the laser diode 810.

[0039] In operation, the photolithography system 100 utilizes the laserdiode 810 to direct light through the lens system 104 (shown as pair oflenses) and onto the mirror 412. The mirror 412 reflects the light ontothe pixel panel 108, which for purposes of illustration is a DMD. Thelight striking the DMD 108 is partially diffracted and scattered,although the scattering and diffraction may be less than that occurringin the system 100 in FIGS. 4a-c due in part to the different lightsources (e.g., laser versus conventional). The DMD 108 may selectivelydirect the light through the series of optical devices 112 and onto thesubstrate 114 (in which case the DMD 108 will be referred to as “on”) ormay direct the light away from the substrate 114 (in which case the DMD108 will be referred to as “off”). The light is to strike the substrate114 at a desired location 812.

[0040] Referring specifically to FIG. 8a, the laser diode 810 is off andso is not projecting light. All the mirrors of the DMD 108 is also offand so light striking the DMD 108 would be reflected away from thesubstrate 114. Referring now to FIG. 8b, the DMD 108 is in a transitionstate between off (FIG. 8a) and on (FIG. 8c). During this transition,the laser diode 810 is off and so no light is projected toward the DMD108. As the DMD 108 is not receiving light from the laser diode 810, theDMD 108 is not directing light toward the substrate 114. Because nolight is being directed toward the substrate 114, there is no blurringeffect as was described previously with respect to the conventionallight source 410 of FIGS. 4a-c. Referring now to FIG. 8c, the transitionperiod of the DMD 108 is complete and the DMD 108 is on. The laser diode810 may be turned on to project light toward the DMD 108, which maydirect the light toward the substrate 114 without blurring. Therefore,the undesirable blurring effect present in the system 100 of FIGS. 4a-cmay be avoided using the laser diode 810 because the laser diode 810does not project light during the DMD 108 transition period.

[0041] Referring now to FIG. 9, in one embodiment, a laser diode outputsignal 910 is shown in non-synchronized operation with a pixel panelstate 912. The laser diode signal 910, which may reflect the operationof a laser diode such as the laser diode 810 of FIGS. 8a-c, may be“high” (indicating that the associated laser diode (not shown) is on,i.e., projecting light) or “low” (indicating that the associated laserdiode is off, i.e., not projecting light). The pixel panel state 912,which may reflect the operation of a pixel panel such as the DMD 108 ofFIGS. 8a-c, may be “on” and “off”. As described previously, “on”indicates that the DMD is reflecting at least a portion of the lightprojected onto it toward a subject. “Off” indicates that the DMD isreflecting the light away from the subject. In the present example,“windows” 914-918 indicate the period of time that the DMD remains on.It is noted that the windows 914-918 could denote the time the DMDremains off, or different windows may be established indicating thestate of the DMD, such as an “on window” and/or an “off window.” Forpurposes of simplification, the transition state is illustrated as beinginstantaneous. This simplification does not alter the describedoperation of the laser diode/DMD combination because the laser diode maybe off during the DMD transition state.

[0042] Synchronization may be difficult and add complexity to theimplementation of systems such as the photolithography system 100 ofFIG. 8. For example, because a window may only exist for a relativelyshort amount of time (i.e., a few hundred microseconds), it may bedifficult to precisely synchronize the laser pulse with the window.Accordingly, the lack of synchronization in the present example enablesthe laser diode signal 910 to pulse at any time during the period whenthe pixel panel state 912 is on.

[0043] In operation, the laser diode signal 910 is generated in pulsemode rather than continuous wave mode. In pulse mode, the associatedlaser diode may be turned on and off multiple times in a single windowto produce pulses 920. Each pulse 920 includes an energy level Δ e and aduration Δ d. The energy level Δ e refers to the amount of energy outputby the laser diode during the particular pulse 920, while the duration Δd indicates the length of time during which the pulse 920 occurs.

[0044] In the present example of FIG. 9, the pulse energy and the pulseduration are constant in the windows 914-918. The duration Δ d of eachpulse 920 is of approximately the same length. Likewise, each pulse 920contains approximately the same amount of energy Δ e. Therefore, anygiven window will have approximately the same pulse energy and pulseduration. It is noted that Δ d and Δ e for each pulse are approximatelyequal, but may vary within a range which has been predetermined asacceptable.

[0045] For binary operation, the total number of pulses 920 in eachwindow 914-918 is fixed (i.e., each window includes the same number ofpulses as the other windows). However, the timing of the pulses 920 in aparticular window 914-920 may be non-synchronous. The timing indicateswhen the pulses 920 occur in the windows 914-918. For example, the fivepulses 920 occur in the window 914 earlier than in the window 916 (i.e.,t₁<t₃ and t₂>t₄). For grayscale operation, the total number of pulses920 may be individually controlled in each window 914-918. Therefore,while the duration Δ d and energy Δ e will be constant for each pulse920, each window may have a different number of pulses 920. For example,the window 914 may have three pulses of duration Δ d and energy Δ e,while the window 916 may have four pulses of the same duration Δ d andenergy Δ e. As with the binary operation, the pulses 920 arenon-synchronous and so the timing of the pulses 920 may vary by window.

[0046] It is noted that in both binary and grayscale operation, thepulses 920 may occur at the same time in the windows 914-918, so that:

[0047] t₁=t₃=t₅.

[0048] Alternatively, none of the pulses 920 may occur at the same timeso that:

[0049] t₁≠t₃≠t₅.

[0050] In addition, certain windows 914-918 may be equivalent whileothers may be unique. Therefore, the non-synchronous approach of thepresent invention enables utilization of both synchronous andnon-synchronous operation as desired.

[0051] Referring now to FIG. 10, in another embodiment, a laser diodeoutput signal 1010 is shown in conjunction with a pixel panel state 1012in a plurality of windows 1016-1018 such as those in FIG. 9. As before,the pixel panel associated with the pixel panel state 1012 is a DMD forpurposes of illustration. However, in the present example, the pulseduration Δ d and the pulse energy Δ e of a plurality of pulses 1020-1036are variable. The duration of each pulse 1020-1036, indicated by Δ d,may vary within a single window 1014-1018. Likewise, the energy Δ e ofeach pulse 1020-1036 may vary within a single window 1014-1016.Therefore, any pulse 1020-1036 in a given window may have a unique pulseenergy Δ e and pulse duration Δ d. It is noted that there may bedesirable minimum and/or maximum limits for the duration Δ d and energyΔ e of each pulse according to a particular application.

[0052] For binary operation, the total amount of energy produced in eachwindow 1014-1018 is fixed (i.e., each window 1014-1018 includes the sameamount of energy as the other windows). Therefore, although the energy Δe of each pulse 1020-1036 may vary, the total energy of the pulses1020-1036 associated with a particular window 1014-1018 should beidentical to the other windows. For example, the pulses 1020-1024 areassociated with the window 1014, and each pulse 1020-1024 may include aunique amount of energy Δ e. Likewise, the pulses 1026, 1028 areassociated with the window 1016, and each pulse 1026, 1028 may include aunique amount of energy Δ e. Because the windows should have the sametotal amount of energy for binary operation, the combined energy Δ e ofthe pulses 1020-1024 should equal the combined energy Δ e of the pulses1026, 1028.

[0053] It is noted that the total energy of a particular window1014-1018 may be produced using pulses of varying duration Δ d as wellas pulse energy Δ e. For example, a level of total energy may beproduced in the window 1014 using a series of low energy pulses havinglong durations. However, the same level of total energy may be producedin the window 1016 using a series of relatively high energy pulseshaving relatively shorter durations. In this manner, the total energyproduced in a window may be produced using a variety of differentcombinations of pulse energy and durations.

[0054] Due to the non-synchronous operation of the laser diode producingthe signal 1010 with the DMD state, the timing of the pulses 1020-1036in the associated window 1014-1018 may vary. For example, the pulses1020-1024 illustrated in the window 1014 are not only different induration and pulse energy than those in the window 1018, but the pulse1020 occurs earlier in the window 1014 than the pulse 1026 in the window1016 (i.e., t₁<t₃). Likewise, the pulse 1024 ends earlier in the window1014 than the pulse 1028 in the window 1016 (i.e., t₂>t₄).

[0055] For grayscale operation, the total amount of energy produced bythe respective pulses in each window 1014-1018 may vary. For example,the total amount of energy delivered by the pulses 1020-1024 in thewindow 1014 may be double the total amount of energy delivered by thepulses 1026,1028 in the window 1016. As in binary operation, the timingof those pulses may vary non-synchronously by window.

[0056] It is noted that in both the binary and grayscale operations ofFIG. 10, one or more of the pulses 1020-1036 may occur at the same timein the windows 1014-1018 or none of the pulses 1020-1036 may occur atthe same time. In addition, certain windows 1014-1018 may be equivalentwhile others may be unique. Therefore, the non-synchronous approach ofthe present invention enables utilization of both synchronous andnon-synchronous operations as desired, and allows the particular pulsecharacteristics for a single window to be tailored to produce a desiredoutput for that window.

[0057] While the invention has been particularly shown and describedwith reference to the preferred embodiment thereof, it will beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention. For example, it is within the scope of the presentinvention to not project light during a period when the DMD is on, andso create a “dark” frame. Therefore, the claims should be interpreted ina broad manner, consistent with the present invention.

1. A method for projecting light onto a subject in an imaging system,the method comprising: providing a light source operable to projectlight in pulses; providing a pixel panel to selectively direct theprojected light towards the subject; determining at least a first periodand a second period during which the pixel panel directs the projectedlight towards the subject, the first and second periods each having astart time; during the first period, projecting the light in at leastone pulse towards the pixel panel at a first time relative to the startof the first period; and during the second period, projecting the lightin at least one pulse towards the pixel panel at a second time relativeto the start of the second period, wherein the first and second timesare not synchronized relative to the start times of the first and secondperiods.
 2. The method of claim 1 further including determining anenergy amount to be produced in each pulse.
 3. The method of claim 1further including determining a duration for each pulse.
 4. The methodof claim 1 further including an end time for each of the first andsecond periods, wherein the end time of the first period occurs beforethe start time of the second period.
 5. The method of claim 4 whereinthe at least one pulse in the first period is of the same duration andenergy as the at least one pulse in the second period.
 6. The method ofclaim 5 wherein there are an equal number of pulses in the first andsecond periods.
 7. The method of claim 4 wherein the at least one pulsein the first period differs in energy from the at least one pulse in thesecond period.
 8. The method of claim 4 wherein the at least one pulsein the first period differs in duration from the at least one pulse inthe second period.
 9. The method of claim 4 wherein there are adifferent number of pulses in the first and second periods.
 10. Themethod of claim 1 further including a third period, wherein no light isprojected towards the pixel panel during the third period.
 11. Animaging system for projecting light onto a subject duringphotolithographic processing, the apparatus comprising: a light sourceoperable to project light in pulses; a pixel panel to selectively directthe projected light towards the subject; a processor connectable to thelight source; a memory accessible to the processor; and software storedin the memory, the software comprising a plurality of instructions for:determining at least a first period and a second period during which thepixel panel directs the projected light towards the subject, the firstand second periods each having a start time; during the first period,projecting the light in at least one pulse towards the pixel panel at afirst time relative to the start of the first period; and during thesecond period, projecting the light in at least one pulse towards thepixel panel at a second time relative to the start of the second period,wherein the first and second times are not synchronized relative to thestart times of the first and second periods.
 12. The system of claim 11wherein the light source is a laser diode operating in pulse mode. 13.The system of claim 11 wherein the software further includesinstructions for regulating the energy produced during each pulse. 14.The system of claim 11 wherein the software further includesinstructions for regulating the duration of each pulse.
 15. A method fornon-synchronously projecting light pulses in a plurality of sequentialperiods in a photolithography system, the method comprising: defining alength of time for each of the plurality of periods, each of the periodshaving a period start time; determining an energy and a duration foreach of the light pulses in each of the periods; and projecting thelight pulses non-synchronously during the plurality of periods, theprojection beginning at a pulse start time after the period start timeof each period, so that wherein the pulse start time for each period isnot synchronized with the pulse start times of the other periods. 16.The method of claim 15 further including setting the energy and durationof each pulse as constant.
 17. The method of claim 16 wherein eachperiod includes a constant number of pulses.
 18. The method of claim 15wherein the sum of pulse energy in each period is equal.